Method For The Production Of Non-Woven, Non-Woven, And Use Thereof

ABSTRACT

The invention relates to a method for the production of non-woven fabrics, in which a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) is spun into a plurality of filament yarns by means of extrusion through a nozzle beam containing a plurality of openings via an air gap into a regenerating bath, said filament yarns being intermingled subsequently by being subjected to a flow with gaseous medium and/or fluid. The invention likewise relates to non-woven fabrics of this type and the use thereof.

The invention relates to a method for the production of non-wovenfabrics, in which a lyotropic solution of cellulose carbamate inN-methylmorpholine-N-oxide (NMMNO) is spun into a plurality of filamentyarns by means of extrusion through a nozzle beam containing a pluralityof openings via an air gap into a regenerating bath, said filament yarnsbeing intermingled subsequently by being subjected to a flow withgaseous medium and/or fluid. The invention likewise relates to non-wovenfabrics of this type and the use thereof.

Non-wovens are textile fabrics, in the case of which the cohesion offibres is ensured not by weaving or knitting but by interlocking andsometimes also by adhesion after intermingling of the fibres. Because ofthe versatile options for use and the low production costs, non-wovenproduction still has high annual growth rates. The advantages of thesenon-woven materials reside in particular in the high moistureabsorption, high variability of density and thickness and also theextensive surface anisotropy, from which the numerous options for usearise, e.g. in medicine (operating sheets, bed sheets, surgicaldressings, gauzes, cotton wool pads etc.), for hygiene products, ashousehold and industrial wipes, as decorative non-woven fabrics(tablecloths, serviettes, curtains), non-woven liners in the clothingindustry and also for numerous technical applications (e.g. insulatingjackets in the building industry).

In principle; non-woven formation from short fibres, staple fibres orcontinuous filament yarns is possible. The methods of non-wovenformation from filament yarns termed as “spunbonding” or as “spunlacing”have the advantage that spinning of the fibres and formation intonon-wovens are effected in one process, and are the subject of thisinvention. A multiplicity of fibre-forming polymers can be used asstarter material for the non-woven fabrics. Non-woven fabrics comprisingcontinuous filaments are produced preferably from synthetic fibres, suchas polyester, polyacrylnitrile or polypropylene. Viscose fibres are usedpreferably as short or staple fibres for non-woven production.

Since the viscose method, with which the largest part of celluloseregenerated fibres is still produced, involves considerableenvironmental damage and high investment costs, comprehensive effortshave been made already for many years to replace the viscose method withalternative methods. This applies also for the production of non-wovenscomprising cellulose. Thus e.g. the so-called “Bemliese” method wasdeveloped, in which cotton linters are spun according to thecuprammonium method and processed into non-wovens (U.S. Pat. No.3,833,438). Both methods have furthermore the advantage that thenon-woven products can be produced from continuous filaments in a directmethod.

Another method, according to which the known “lyocell” fibre inter aliais produced, resides in precipitation of a solution of cellulose in asystem comprising N-methylmorpholine-N-oxide (NMMNO) and water (U.S.Pat. No. 3,767,756, DE 28 30 685), the solution being extruded into anaqueous regenerating bath via an air gap. The method is also used forthe production of non-woven products (WO 00/18991, WO 98/07911).

A further known method for the production of fibres and other mouldedarticles comprising regenerated cellulose resides in the precipitationof a solution of cellulose carbamate (EP-A 57 105, EP-A 178 292) whichis formed by conversion of cellulose with urea, with thermal cleavage ofthe urea into isocyanic acid and ammonia and reaction of the isocyanicacid with the OH groups of the cellulose. Cellulose carbamate is solublein cold dilute sodium hydroxide solution and can be regenerated againinto cellulose in heated sodium hydroxide solution.

Starting herefrom, it was the object of the present invention to providea method independent of the viscose method for the production ofnon-woven fabrics comprising cellulose carbamate or regeneratedcellulose, which fulfils the requirements with respect to low investmentand production costs and also low environmental damage with good productproperties. It was likewise the object of the invention to providenon-woven fabrics with superior product properties.

This object is achieved by the method having the features of claim 1 andthe non-woven fabrics having the features of claims 20 and 23. Thefurther dependent claims reveal advantageous developments. In claims 28to 33, uses of the non-woven fabric according to the invention areindicated.

According to the invention, this object is achieved in that a lyotropicsolution of cellulose carbamate in. N-methylmorpholine-N-oxide (NMMNO)is spun into a plurality of filament yarns by means of extrusion througha nozzle block containing at least 20 openings, i.e. nozzles, via an airgap into a regenerating bath, said filament yarns being intermingledsubsequently by being subjected to a flow with gaseous medium and/orfluid forming the non-woven fabric.

Cellulose carbamate is soluble in NMMNO and can be shaped in a similarmanner to cellulose. Relative to the conventional NMMNO method, thefollowing advantageous differences are thereby revealed.

-   -   1. The viscosity of the solution increases greatly with        increasing content of cellulose or cellulose carbamate. Too high        a viscosity however impairs the spinnability of the solution.        The limit of the spinnability is therefore, in the conventional        cellulose solution, at a content of at most 15%. In contrast,        this limit with cellulose carbamate is at approx. 30%. Solutions        with a content of cellulose carbamate of 25% can still be spun        without problem. The higher concentration of the solution causes        lower use of solvent and hence lower expense in the reprocessing        of the regenerating bath in order to recover the NMMNO and thus        leads to a significant cost reduction.    -   2. Solutions with a cellulose carbamate content of over 20%        surprisingly reveal a lyotropic behaviour, i.e. the cellulose        carbamate is present in a liquid-crystalline state, as is        evident from polarising microscopic pictures (pictures 1 and 2).        The extremely advantageous application is produced therefore        that the molecules are orientated virtually perfectly in the        fibre direction during spinning as a result of the shearing in        the nozzle channel, the fibres thus have an extraordinarily high        orientation and hence very high strength. Strengths of 60 cN/tex        and above are achievable.    -   3. Cellulose carbamate has a substantially higher water        absorption capacity and better colouring capacity than        cellulose.

Preferably a nozzle beam with at least 10,000 openings is used for theextrusion. The ratio of length to diameter (L/D ratio) of the nozzles isthereby preferably between 1 and 20.

Preferably, the width of the air gap between nozzle and regeneratingbath is 5 to 250 mm, particularly preferred 10 to 150 mm.

In a preferred embodiment variant of the method, the filament yarns areguided downwards after spinning into a slot-shaped funnel, theintermingling with the gaseous medium and/or fluid being effected at theoutlet of the funnel. In order to improve the intermingling of thefilament yarns, it is preferred furthermore to produce this by means ofa shaking movement of the funnel.

Preferably air and/or water are used as gaseous medium and/or fluid.

It is preferred furthermore that the filament yarns are laid on aconveyor belt after the intermingling. Preferably, a furtherintermingling of the filament yarns is achieved thereby by a shakingmovement of the conveyor belt.

Preferably, the lyotropic solution is produced by swelling of thecellulose carbamate in a 50% solution of NMMNO in water and subsequentremoval of the water up to a ratio of NMMNO to water between 80:20 and90:10, particularly preferred 87:13.

The cellulose carbamate proportion of the lyotropic solution is therebypreferably at least 20% by weight, particularly preferred 22 to 27% byweight. The percentage details hereby relate to the entire lyotropicsolution.

Preferably, the regenerating bath comprises a solution of NMMNO in waterwith an NMMNO proportion of 0.5 to 25% by weight, particularly preferred5 to 15% by weight, relative to the solution of NMMNO in water.

The extrusion or spinning is effected preferably at a temperature of 80to 110° C., particularly preferred from 85 to 95° C.

In a further advantageous embodiment variant of the method, thenon-woven fabric is washed subsequent to the above-described steps,pressed and dried. The washing can thereby be effected preferably by awater jet at high pressure.

It is preferred furthermore if the cellulose carbamate is regeneratedinto cellulose in a regenerating bath comprising 0.3 to 1% by weightsodium hydroxide in water at a temperature of 60 to 95° C. It is madepossible as a result to produce non-woven fabrics from regeneratedcellulose. It is possible in a first advantageous variant to implementthe regeneration between extrusion and intermingling. A furtherpreferred variant provides that the regeneration is implemented afterthe intermingling.

According to the inevention, a non-woven fabric is likewise providedfrom a random orientation of filament yarns made of cellulose carbamate.It is thereby preferred if the filament yarns have a strength of 60cN/tex. Furthermore, a non-woven fabric of this type can be producedpreferably according to the method according to one of the claims 1 to19.

According to the invention, a non-woven fabric is also produced from arandom orientation of filament yarns made of regenerated cellulose. Withrespect to the regeneration of the cellulose carbamate into cellulose,reference is thereby made to claims 16 to 19. The fibres made ofregenerated cellulose thereby preferably have a residual nitrogencontent (residual N-content) of 0.3 to 0.5, particularly preferred from0.1 to 1.2.

The non-woven fabric has a pore structure with a preferred porosity of 1to 10%.

It is furthermore preferred if the non-woven fabric has a specificinternal surface between 20 and 50 m²/cm³, measured by means of smallangle x-ray scattering (SAXS).

It is particularly preferred if the non-woven fabric according to theinvention can be produced from regenerated cellulose according to themethod according to one of the claims 16 to 19.

The non-woven fabrics according to the invention are used preferably inmedicine, in particular as operating sheets, bed sheets, surgicaldressings, gauzes or cotton wool pads. Likewise the non-woven fabricscan also be used as hygiene materials or as household wipes. A furtherapplication field of the non-woven fabrics according to the invention isthat of decorative non-woven fabrics, in particular tablecloths,serviettes or curtains and also non-woven liners in the clothingindustry. Furthermore, the non-woven fabrics according to the inventionare used as insulating jackets or reinforcing mats, e.g. as areplacement for glass fibre mats in the building industry. Because ofthe high strength, the non-woven fabrics according to the invention canbe used, similarly to glass fibre mats, for reinforcement of plasticmaterials.

The subject according to the invention is intended to be explained inmore detail with reference to the subsequent Figures and the subsequentexample without restricting said subject to the embodiment variantsdescribed herein.

FIG. 1 shows a schematic representation of the course of the methodaccording to the invention.

FIG. 2 shows a slot-shaped funnel according to the invention, at theoutlet of which the intermingling is effected.

The basic course of the method is illustrated in FIG. 1. The spinningsolution 1 is hereby extruded into a regenerating bath 4 via a spinningpump 2 by means of a nozzle beam 3 which contains a multiplicity ofnozzles. The spinning is thereby effected vertically from the top to thebottom via the air gap into the regenerating bath. The fibres are drawnoff in the horizontal direction via deflection rollers 5. On thisstretch, a first washing bath and an elongation stretch can optionallybe situated. A further deflection roller 6 guides the fibre bundlesubsequently downwards into a slot-shaped funnel 7, at the outlet ofwhich the fibre bundle is subjected on both sides to a flow of air orwater. The thus intermingled fibres are laid on the conveyor belt 8situated thereunder, a further intermingling being effected by a shakingmovement of the laying device or of the conveyor belt transverselyrelative to the running direction. The belt passes through a washingbath with a washing nozzle 9 which can also be produced by a water jetat high pressure, and hence leads to further compaction of the materialin the sense of spunlacing. The conveyor belt comprises a wide-mesh netpreferably made of metal, which ensures rapid discharge of the washingliquid. Subsequently, the material can be dried in corresponding dryingdevices. The water can however also be pressed out by a pair of rollerswith which compaction of the non-woven fabric can be achieved at thesame time.

FIG. 2 shows the construction of a slot-shaped funnel according to theinvention. The fibre can be introduced into the mentioned funnel via thefibre inlet 1. Conveyance of the fibre through the funnel is therebymade possible by a Venturi nozzle which replaces the water jetprinciple. The supply of water, air or also a mixture thereof iseffected through the opening 3, which, because of the Venturi profile,flows past the channel 4 such that a low pressure is produced whichconveys the fibre through the channel 4. At the lower end 5 of thefunnel there is situated the fibre outlet from where the filament yarnscan then be conveyed further.

EXAMPLE

800 g pulp with a DP_((cuoxam)) of 520 are mixed intensively in akneader with 3,200 g of a solution, comprising 12% by weight NaOH, 30%by weight urea and 58% by weight water for 1 h at 25° C. andsubsequently is ripened at 23° C. for 48 h to a DP_((cuoxam)) of 300.The moist alkali cellulose is kneaded for 30 min. at room temperature ina 5 l kneader with 1200 g solid crystalline urea. Subsequently thetemperature of the kneader is increased to 140° C. and the water whichis present is drawn off. After reaching a product temperature of 140°C., the mass is kneaded further for 120 min. and subsequently dischargedfrom the kneader. In order to obtain the pure CC, the dry crumbly massis washed 3 times with de-ionised water at a liquor ratio of 1:16, issuctioned off via a frit and then dried at room temperature. This looseand crumbly product had a nitrogen content of 3.0% and a DP_((cuoxam))of 290.

The cellulose carbamate was mixed in a kneader with a 50% aqueous NMMOsolution, this solution was concentrated by withdrawing the excess waterin a vacuum of 80 mbar and concentrated up to NNMO monohydrate andthereby the cellulose carbamate was dissolved. The spinning solution hada cellulose content of 25% by mass. The solution was spun on alaboratory unit with 10,000 capillaries, guided to the interminglingnozzle via a roller system, intermingled there in a water flow and laidcontinuously on a conveyor belt to form a non-woven, washed and dried.The basis weight of the non-woven was 75.7 g/m², the dry strength 8.5kN/m.

1. Method for the production of non-woven fabrics, in which a lyotropicsolution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) isspun into a plurality of filament yarns by means of extrusion through anozzle block containing at least 20 openings via an air gap into aregenerating bath, said filament yarns being intermingled subsequentlyby being subjected to a flow with gaseous medium and/or fluid.
 2. Methodaccording to claim 1, characterised in that a nozzle block with at least10,000 openings is used.
 3. Method according to claim 1, characterisedin that the ratio of length to diameter of the nozzles is from 1 to 20.4. Method according to claim 1, characterised in that the width of theair gap between nozzle and regenerating bath is 5 to 150 mm, inparticular 10 to 50 mm.
 5. Method according to claim 1, characterised inthat the filament yarns are guided downwards after spinning into aslot-shaped funnel, the intermingling with the gaseous medium and/orfluid being effected at the outlet of the funnel.
 6. Method according toclaim 5, characterised in that a further intermingling of the filamentyarns is achieved by a shaking movement of the funnel.
 7. Methodaccording to claim 1, characterised in that air and/or water are used asgaseous medium and/or fluid.
 8. Method according to claim 1,characterised in that the filament yarns are laid on a conveyor beltafter the intermingling.
 9. Method according to 8, characterised in thata further intermingling of the filament yarns is achieved by a shakingmovement of the conveyor belt.
 10. Method according to claim 1,characterised in that the cellulose carbamate proportion of thelyotropic solution is at least 20% by weight, in particular 22 to 27% byweight, relative to the solution.
 11. Method according to claim 1,characterised in that the lyotropic solution is produced by swelling ofthe cellulose carbamate in a 40 to 70%, in particular a 50% solution ofNMMNO in water and subsequent removal of the water up to a ratio ofNMMNO to water between 80:20 and 90:10.
 12. Method according to claim 1,characterised in that the regenerating bath comprises a solution ofNMMNO in water with an NMMNO proportion of 0.5 to 25% by weight, inparticular 5 to 15% by weight, relative to the solution.
 13. Methodaccording to claim 1, characterised in that the extrusion is effected ata temperature between 80 to 110° C., in particular 85 to 95° C. 14.Method according to claim 1, characterised in that the non-woven fabricis subsequently washed, pressed and dried.
 15. Method according to claim14, characterised in that the washing is effected by a water jet at highpressure.
 16. Method according to claim 1, characterised in that thecellulose carbamate is regenerated into cellulose in a regeneratingbath.
 17. Method according to claim 16, characterised in that theregenerating bath comprises 0.3 to 1% by weight sodium hydroxide inwater and the regeneration is effected at a temperature of 60 to 95° C.18. Method according to claim 16, characterised in that the regenerationis implemented between extrusion and intermingling.
 19. Method accordingto claim 16, characterised in that the regeneration is implemented afterthe intermingling.
 20. Non-woven fabric comprising a random orientationof filament yarns made of cellulose carbamate.
 21. Non-woven fabricaccording to claim 20, characterised in that the filament yarns have astrength of at least 60 cN/tex.
 22. Non-woven fabric according to claim20, characterised in that the non-woven fabric can be produced accordingto the method according to a method for the production of non-wovenfabrics, in which a lyotropic solution of cellulose carbamate inN-methylmorpholine-N-oxide (NMMNO) is spun into a plurality of filamentyarns by means of extrusion through a nozzle block containing at least20 openings via an air gap into a regenerating bath, said filament yarnsbeing intermingled subsequently by being subjected to a flow withgaseous medium and/or fluid.
 23. Non-woven fabric comprising a randomorientation of filament yarns made of regenerated cellulose. 24.Non-woven fabric according to claim 23, characterised in that theresidual N-content is from 0.3 to 0.5%, in particular 0.1 to 0.2%. 25.Non-woven fabric according to claim 23, characterised in that thenon-woven fabric has a pore structure with a porosity of 1 to 10%. 26.Non-woven fabric according to claim 23, characterised in that thenon-woven fabric has a specific internal surface between 20 and 50m²/cm³, measured by means of small angle x-ray scattering (SAXS). 27.Non-woven fabric according to claim 23, characterised in that thenon-woven fabric can be produced with a method for the production ofnon-woven fabrics, in which a lyotropic solution of cellulose carbamatein N-methylmorpholine-N-oxide (NMMNO) is spun into a plurality offilament yarns by means of extrusion through a nozzle block containingat least 20 openings via an air gap into a regenerating bath, saidfilament yarns being intermingled subsequently by being subjected to aflow with gaseous medium and/or fluid characterised in that thecellulose carbamate is regenerated into cellulose in a regeneratingbath.
 28. Use of the non-woven fabrics according to claim 20 inmedicine, in particular as operating sheets, bed sheets, surgicaldressings, gauzes or cotton wool pads.
 29. Use of the non-woven fabricsaccording to claim 20 as hygiene materials or as household wipes. 30.Use of the non-woven fabrics according to claim 20 as decorativenon-woven fabrics, in particular tablecloths, serviettes or curtains.31. Use of the non-woven fabrics according to claim 20 as non-wovenliners in the clothing industry.
 32. Use of the non-woven fabricsaccording to claim 20 as reinforcing mats or isolating jackets in thebuilding industry.
 33. Use of the non-woven fabrics according to claim20 as reinforcing material for fibre-reinforced thermoplastic andduroplastic plastic materials.